Vacuum circuit interrupter contacts



April 19, 1966 Filed June 5 1965 J. M. LAFFERTY ET AL 3,246,979 VACUUM CIRCUIT INTERRUPTER CONTACTS 4 Sheets-Sheet 1 //v vz/vra/ws JAML-S M. L/IFFE/UV,

PH/A m EAR/(AN, THOMAS H. 455, mag/w 4. m4 5/1/70,

April 19, 1966 J. M. LAFFERTY ET AL. 3,246 7% VACUUM CIRCUIT INTERRUPTER CONTACTS Filed June 5, 1963 Sheets-Sheet 2 ATTORNEY.

April 19, 1966 LAFFERTY ET AL 3,246,979

VACUUM CIRCUIT INTERRUPTER CONTACTS 4 Sheets-Sheet 5 Filed June 5, 1965 22m 6 F K L FP .A AA T 715 N 0 L V MWWH NJMO April 19, 1966 LAFFERTY ET AL 3,246,979

VACUUM CIRCUIT INTERRUPTER CONTACTS 4 Sheets-Sheet Filed June 5, 1963 uvvavrom:

JAMES M. LAFFE/wx PH/L/P BflR/(A/V. THOMAS H. LEE.

JOSEPH L. TALE/V70.

ATTORNEY.

United States Patent 3,246,979 VACUUM CIRCUIT INTERRUPTER CDNTACTS James M. Laii'erty, Schenectady, N.Y., and Philip Barkan and Thomas H. Lee, Media, and Joseph L. Talento,

Drexel Hill, Pa, assignors to General Electric Company, a corporation of New York Filed June 3, 1963, Ser. No. 286,127 23 Claims. (Cl. 75-134) This application is a continuation-in-part of our application S.N. 151,552, filed November 10, 1961, now abandoned and assigned to the assignee of the present invention.

This invention relates to a vacuum-type circuit interrupter and, more particularly, to contact structure for such an interrupter. The invention is especially, though not exclusively, concerned with contact structure for a vacuum-type circuit interrupter having a voltage rating of at least 7.2 kilovolts and a current interrupting rating of at least 8,000 amperes.

In certain of its broader aspects, the invention is applicable to interrupters having lower voltage and current ratings; but to facilitate an understanding of the invention, emphasis in the descriptive portion of this application will be placed on its applicability to circuit interrupters having a voltage rating of at least 7.2 kilovolts and a current interrupting rating of at least 8000 amperes.

There are three basic requirements that must be met for oilless circuit breakers or interrupters of such rating. The first of these is that the circuit breaker must be capable of withstanding, without damage or a disruptive discharge, an impulse crest voltage of at least 95 kv. and a continuous 60 cycle voltage of at least 36 kv. R.M.S. each of these voltages being applied across its fullyopen contacts. The impulse voltage is applied as a standard wave which rises to crest in 1.5 microseconds and drops to half crest value in 40 microseconds. This first requirement shall be referred to hereinafter as the dielectric strength requirement. The dielectric strength figures specified are taken from Part2, page of the National Electrical Manufactures Association (NEMA) Standards for Power Circuit Breakers, Publication SG4 1954, March 1954, Revised November .1955. A second requirement is that the interrupter be capable of interrupting 8000 amperes R.M.S. at rated voltage. This requirement shall be referred to hereinafter as the interrupting ability requirement. The third requirement is that the interrupter be capable of carrying and closing against momentary currents substantially in excess of its rated interrupting current without producing objectionable welds between its contacts and without otherwise damaging its contacts. This third requirement will be referred to hereinafter as the antiweld requirement. ing this third requirement, it is important to prevent the formation not only of those welds that are so strong that they cannot be broken except with excessive force during a subsequent opening operation but also those welds that cannot be fractured cleanly and without production of a jagged interface between the two contacts. The production of such a jagged interface leads to excessive contact wear and also to reduced dielectric strength. This anti-weld requirement is especially difiicult to meet in a Vacuum type circuitbreaker because the contacts of such interrupters must be extremely clean and have surfaces devoid of oxide and other contaminating .films. These clean surface conditions are ideal for the production of objectionable welds, which in many cases would be largely avoided if oxide or other contaminating films were present at the interface.

Efforts to meet all three of these basic requirements with a single-break vacuum-type circuit interrupter have heretofore been unsuccessful because, insofar as we are In meet- "Ice aware, no contact materials have been found which can meet all three of these requirements in a single-break vacuum interrupter. Materials that have been found capable of meeting one, or even two, of these requirements have failed to meet the remaining requirement or requirements.

Accordingly, an object of our invention is to provide a single-break vacuum-type circuit interrupter that is capable of meeting all three of these requirements as they exist for an interrupter having a rated voltage of at least 7.2 kv. and a rated current interrupting capacity of at least 8000 amperes R.M.S.

In carrying out our invention in one form, we provide, in a vacuum-type circuit interrupter having a rated voltage of at least 7.2 kv. a pair of contacts that are relatively movable into and out of engagement. The contacts have circuit-making regions that serve also as circuit-breaking regions during opening. These regions are substantially free of all absorbed gases and surface contaminants andare formed of an alloy consisting essentially of a major constituent and a minor constituent, with the minor constituent being highly dispersed throughout the alloy. The major constituent is a non-refractory metal having a boiling point less than 3,5(l0 K. and the minor constituent is a non-refractory metal that (1) has an effective freezing temperature below that of the major constituent (2) has substantial solubility in the major constituent in the liquid state and (3) has little or no solubility in the major constituent in the solid state. With regard to requirement (3), the solubility of the minor constituent in the major constituent should be below 2% by weight w of the alloy at a controlling temperature corresponding either to the eutectic temperature of the alloy or to the freezing temperature of the minor constituent if there is no eutectic. We have discovered that the dielectric strength of an interrupter that uses this type of contact material can be unexpectedly improved if the percentage of the minor constituent that is present is limited to a critically low value. For this reason, the percentage of this latter metal is limited to a value small enough to maintain the dielectric strength of the interrupter above kv. peak impulse voltage and 36 kv. R.M.S. 60 cycle withstand voltage, both voltages being applied across said two contacts when fully-open. The minimum amount of minor constituent present must be substantially above the solid state solubility of the minor constituent in the major constituent at said controlling temperature.

Examples of materials satisfying the above requirements are alloys of copper and small percentages of a minor constituent selected from the group consisting essentially of tellurium, bismuth, lead, and thallium; al-

loys of silver and small percentages of a minor constituent selected from the group consisting essentially of bismuth, lead, and tellurium; and alloys of aluminum and small percentages of a minor constituent selected from a group consisting essentially of lead, indium and tin.

The percentage by weight of the minor constituent in each of these alloys is made small enough to hold the dielectric strength of the interrupter above the withstand voltages set forth hereinabove. By way of example and not limitation, suitable percentages of the minor constituent are a few percent or lower by weight of the total weight of the alloy.

For a better understanding of our invention, reference may be had to the following description taken in conjunction with the accompanying illustrations, wherein:

FIG. 1 is a sectional view of a vacuum-type circuit interrupter embodying our invention.

FIG. 2 is an enlarged perspective view of one of the contacts of the interrupter of FIG. 1.

FIG. 3 is a photomicrograph at 500x magnifications of the grain structure of a copper-bismuth alloy contain- Patented Apr. 19, 1956:

o ing 20% bismuth by weight. g The alloy is depicted in its as-ca'st form. i 7

FIG. 4 is a photomicrograph similar to FIG. 3 but for a copper-bismuth alloy containing 15% bismuth by weight.

FIG. 5 is a photomicrograph similar to for a copper-bismuth alloy containing 11% weight.

FIG. 6 is a photomicrograph similar to for a copper-bismuth alloy containing 5% weight.

FIG. 7 is a photomicrograph similar to for a copper-bismuth alloy containing 1% weight.

FIG. 8 is a photomicrograph similar to for a copper-bismuth alloy containing .5 weight.

FIG. 9 is a photomicrograph at 100x magnifications of the grain structure of a copper-lead alloy containing 1% lead by weight. The alloy is depicted in its as-cast form.

FIG. 10 is a photomicrograph of the same material as depicted in FIG. 9 but at a magnification of 500x.

FIG. 11 is a photomicrograph at 750 magnifications of a portion of a contact taken in a cross-sectional plane generally perpendicular to the surface of the contact that engages the opposite contact. The depicted contact has been closed against a heavy current to produce a weld and then separated from the other contact under nocurrent conditions to break the weld.

Referring now to the interrupter of FIG. 1, there is shown a highly evacuated envelope 10 comprising a casing 11 of a suitable insulating material, such as glass or alumina, and a pair of metallic end caps 12 and 13, closing off the ends of the casing. Suitable seals 14 are provided between the end caps and'the casing to render the envelope 10 vacuum tight. The normal pressure within the envelope 10 under static conditions is lower than 10- mm. of mercury so that a reasonable assurance is had that the mean free path for electrons will be longer than the potential breakdown paths in the envelope.

The internal insulating surfaces of casing 11 are protected from the condensation of arc-generated metal vapors thereon by means of a tubular metallic shield 15 suitably supported on the casing 11 and preferably iso lated from both end caps 12 and 13. This shield acts in a well-known manner to intercept arc-generated metallic vapors before they can reach the casing 11.

Located within the envelope 10 is a pair of separable contacts 1'7 and 18, shown in their engaged or closedcircuit position. The upper contact 17 is a stationary contact suitably attached to a conductive rod 17a, which at its upper end is united to the upper end cap 12. The lower contact 18 is a movable contact joined to a. conductive operating rod 18a which is suitably mounted for vertical movement. Downward motion of the contact 18 separates the contacts and opens the interrupter, whereas return movement of contact 18 reengages the contacts and thus closes the interrupter. A typical gap length when the contacts are fully-open is about /2 inch. The operating rod 18a projects through an opening in the lower end cap 13, and a flexible metallic bellows 20 provides a seal about the rod 18a to allow for vertical movement of the rod without impairing the vacuum inside the envelope 10. As shown 'in FIG. 1, the bellows 20 is secured in sealed relationship at its respective opposite ends to the operating rod 18:: and the lower end cap 13.

All of the internal parts of the interrupter are substantially free of surface contaminants. These clean surfaces are obtained by suitably processing the interrupter, as by baking it out during its evacuation. A typical bakeout temperature is 400 C. In addition, the contacts 17 and 18 are effectively freed of gases absorbed internally of the contact body so as to preclude evolution of these gases during high current arcing. The manner in which FIG. 3 but FIG. 3 but bismuth by FIG. 3 but bismuth by FIG. 3 but bismuth by bismuth by these internal gases are removed will be referred to in more detail hereinafter.

Although our invention is not limited to any particular contact configuration, we prefer to use the contact configuration disclosed and claimed in US. Patent 2,949,520, Schneider, assigned to the assignee of the present invention. Accordingly, each contact is of a disk shape and has one of its major surfaces facing the other contact. The central region of each contact is formed with a recess 29 in this major surface and an annular contact-making area 30 surrounds this recess. These annular contact-making areas 30 abut against each other when the contacts are in their closed position of FIG. 1, and are of such a diameter that the current flowing through the closed contacts follows a loop-shaped path L, as is indicated by the dotted lines of FIG. 1. Current flowing through this loopshaped path has a magnetic effect which in a well known manner to lengthen the loop. As a result, when the contacts are separated to form an are between the areas 30, the magnetic effect of the current flowing through the path L will impel the arc radially outward.

As the arc terminals move toward the outer periphery of the disks 17 and 18, the arc is subjected to a circumferentially-acting magnetic force that tends to cause the arc to move circumferentially about the central axes of the disk. This circumferentially-acting magnetic force is preferably produced by a series of slots 32 provided in the disks and extending from the outer periphery of the disks radially inward by generally spiral paths, as is shown in FIG. 2. These slots 32 correspond to similarly designated slots in the aforementioned Schneider patent and, thus, force the current flowing to or from an arc terminal located at substantially any angular point on the outer peripheral region of the disk to follow a path that has a net component extending generally tangentially with respect to the periphery in the vicinity of the arc. This tangential configuration of the current path results in the development of a net tangential force component, which tends to drive the arc in a circumferential direction about the contacts. In certain cases, the arc may divide into a series of parallel arcs, and these parallel arcs move rapidly about the contact surface in a manner similar to that de scribed hereinabove.

One of the problems that the present invention is concerned with is providing a single-break vacuum-type circuit breaker or interrupter of the general type described up to this point that is capable of meeting the conventional specification for an oilless circuit breaker having a voltage rating of at least 7.2 kv. and an interrupting rating of at least 8,000 amperes. As pointed out hereinabove, there are three basic requirements which such breakers must be capable of meeting-the dielectric strength requirement, the interrupting ability requirement, and the anti-weld requirement. With respect to the dielectric strength requirement, the breaker must be capable of withstanding without breakdown an impulse crest voltage of at least kv. and a continuous 60 cycle voltage of at least 36 kv. R.M.S. each of these voltages being applied across its contacts in their fully-open position. A typical gap length when the contacts are fully-open is about /z inch. In general, the invention is concerned with gap lengths less than about one inch. With respect to the interrupting ability requirement, the breaker must be capable of interrupting 8,000 ampres R.M.S. at rated voltage. With respect to the anti-weld requirement, the breaker must be capable of carrying and closing against momentary currents substantially in excess of its rated interrupting current without producing strong welds between its contacts or welds which break with a jagged fracture upon opening. 0

Efforts to meet these three basic requirements with a single-break vacuum-type circuit breaker have heretofore been unsuccessful because, insofar as we are aware, no

meeting one or even two of these requirements have failed to meet the remaining requirements. For example, contacts made of a highly refractory material such as tungsten can meet the dielectric strength requirement and the anti-weld requirement, but are completely inadequate to meet the interrupting ability requirement. As another example, contacts made of copper can meet the interrupting ability requirement and the dielectric strength re. quirement but are inadequate to meet the anti-weld requirement. Contacts made of copper alloyed with tin and with zinc, i.e., the bronzes and brasses, have been able to meet the interrupting ability requirement and in some cases the dielectric requirement but still not the anti-weld requirement. As another example, contacts formed from certain of the materials disclosed and claimed in U.S. Patent No. 2,975,225, Laiferty, assigned to the assignee of the present invention, have been able consistently to meet the interrupting ability requirement and the anti-weld requirement, but not the dielectric strength requirement. One contact material disclosed in the Lafierty patent which is in this latter category is a copperbismuth alloy containing to 35% bismuth. Though adequate to meet the interrupting ability requirement and the anti-weld requirement, this material, at least when processed by known techniques, has not been able to consistently meet the dielectric strength requirement.

We have found that all three of these requirements can be met inthe interrupter of the present invention by forming the contacts of an alloy that consists essentially of a major constituent that is a non-refractory metal, preferably, of good electrical conductivity, having a boiling point less than 3,500 K., and a minor constituent that: (1) has an effective freezing temperature below that of the major constituent, (2) has substantial solubility in the major constituent in the liquid state and (3) has little or no solubility in the major constituent in the solid state, i.e., has a solid state solubility below 2% by weight of the alloy, considered at a controlling temperature corresponding to the eutectic temperature of the alloy or the freezing temperature of the minor constituent if there is no eutectic. The minor constituent, in addition to meeting these three requirements, is highly dispersed throughout the alloy. The maximum percentage of the minor constituent that is present in the alloy must be limited to a relatively low value that is small enough to maintain the dielectric strength of the interrupter above 36 kv. R.M.S. 6O cycle withstand volt age and 95 kv. impulse crest voltage. The minimum percentage of the minor constituent should be substantially above a value corresponding to the solid state solubility of this minor constituent in the major constituent at said controlling temperature. To illustrate this latter requirement as it applies to a copper-bismuth alloy, the amount of bismuth present in the copper should be above .02% by weight, which exceeds the best available estimate of the solid state solubility of bismuth in copper at the eutectic temperature 270 C. To assure compliance with this latter requirement, we prefer that the minimum percentage of bismuth present be about .05 Examples of alloys that meet the above-stated requirements are: copper-bismuth, copper-lead, copper-tellurium, copper-thallium, silver-bismuth, silver-lead, silver-tellurium, aluminum-lead, aluminum-indium, and aluminumtin, with the secondary, or minor, constituent of each of these alloys being present in amounts exceeding their solid state solubility but still in small percentages, e.g., a few percent or less by weight of the total alloy weight. In the above listing of alloys and in all other similar references to alloys in the application, the major, or primary, constituent is specified first and the minor, or secondary, constituent next.

With regard to the percentages of the minor constituent that must be included in the mixture, it does not presently appear to be possible to set forth precise numerical limits which would govern for all of the mixtures claimed herein. One reason for this is that these percentages vary somewhat from one material to the next. Another reason for this is that precise data on solubility as to all of these materials is not presently available. However, one skilled in this art, given our teaching that small amounts of the claimed minor constituents can be included in the claimed major constituents to produce the desired anti-weld properties without significantly impairing the dielectric strength properties of the material, should have no difiiculty in arriving at a suitable small percentage.

In preparing these contact materials, each separate constituent first should be suitably processed to free it of sorbed gases and other contaminants, as, for example, by the zone-refining process described in application S.N. 854,392, Hebb, filed November 20, 1959, and assigned to the assignee of the present invention. The two constituents are then melted and thereafter thoroughly mixed together while they are in the liquid state, after which the temperature of the mixture is lowered to cause the constituents to solidify or freeze in a manner described in more detail hereinafter. The material that results upon freezing in this manner, we refer to as the as cast material.

Metallographic studies have been made in an effort to establish whether there are any structural differences in the contact materials that are acceptable from a dielectric strength and anti-weld viewpoint and those that are unacceptable in these respects. In studying the contact materials in their as cast form, one distinction that appears significant was observed. This distinction was in the structure of the boundaries between the grains of the major, or primary, constituent. More specifically, in the acceptable materials definite deposits of the minor, or secondary, constituent were found to be present in these grain boundaries, but, typically, in amounts insufficient to cause a thick continuous deposit of the minor constituent along these grain boundaries. In some of the unacceptable materials, particularly those unacceptable from an anti-weld viewpoint, there was generally no significant amount of minor constituent present in the grain boundaries. In others of the materials that were unacceptable, particularly from a dielectric strength viewpoint, there was minor constituent present in the grain boundaries, but generally in the form of a thick continuous deposit, as contrasted to the absence of such a thick continuous deposit in the acceptable materials. In referring to a thick deposit, we means a deposit having a thickness in excess of about 5X10- inches. In the acceptable materials, the grain boundaries generally include some discrete particles of a secondary constituent having a thickness in excess of this figure of 5 10 inches, but, typically, these particles are sufiieiently spaced to preclude the formation of a continuous deposit along the grain boundary with a thickness exceeding 5 X10" inches. A generally continuous film with a thickness substantially below this value may be present along the grain boundaries in some of the acceptable materials, but our studies indicate that films of this reduced thickness are not objectionable.

These characteristics of the grain structure can be better understood by referring to FIGS. 3-8, which are photomicrographs taken at a magnification of 580x of the grain structure in copper-bismuth contacts, in their as cast form, having various percentages of bismuth as a minor constituent. Referring first to FIGS. 3-5, there are shown copper-bismuth alloys in which unacceptably large amounts of bismuth are present. FIG. 3, for example, illustrates the grain structure for an alloy containing 20% bismuth. It can be seen in FIG. 3 that the copper grains 5% are surrounded by a relatively thick deposit 52 of bismuth. This bismuth deposit has an average thickness of about 15 to 20 10 inches and extends generally continuously about each grain boundary. In FIGS. 4 and 5 which illustrate the grain structure for copper-bismuth alloys containing 15% and 11% bismuth, respectively, the generally continuous thick deposit of bismuth is still present along the boundaries between the copper grains 54). The bismuth deposit in the 11% bismuth alloy has a lesser thickness than in the 15% bismuth alloy, but its average thickness is still about 12 l0 inches, and thus is still considered a thick deposit, as defined hereinabove. These alloys of FIGS. 3-5, although adequate from an anti-weld viewpoint, have been found incapable of meeting the dielectric strength requirements set forth hereinabove. FIGS. 6, 7, and 8 are photomicrographs at 560x magnifications of copper-bismuth alloys that have been found acceptable in meeting the three basic requirements set forth hereinabove. Referring now to FIG. 6, which illustrates a copper-bismuth alloy containing 5% bismuth, it can be seen that there are relatively thick particles 54 of bismuth present in the boundaries between the copper grains, but these particles are discrete and sufficiently separate to preclude the presence of a continous thick deposit over a substantial portion of the grain surface. There is a thin film 52 present along the grain boundary, but this film has an average thickness less than 5 l0- inches and therefore cannot be classed as a thick deposit as defined hereinabove. With the copper-bismuth alloy containing 1% bismuth, depicted in FIG. 7 there are still some particles 54 of substantial thickness, but these, too, are discrete and sufiiciently separate to preclude the presence of a continous thick deposit. A very thin film of bismuth may, however, still be present along the grain boundaries, as indicated at 56. A copper-bismuth alloy containing 0.5% bismuth is depicted in FIG. 8. This alloy, like that of FIG. 7, contains particles of bismuth in the grain boundaries and traces of a bismuth film 56 along the boundaries, but this film is clearly not a thick deposit as defined hereinabove.

To provide additional illustrations of the character of the grain structure in the contact materials of our invention, FIGS. 9 and 10 are included. These are photomicrographs of a copper-lead alloy including one percent lead by weight. FIG. 9 is at a magnification of 100x, and FIG. 10 is at a magnification of 500x. It will be apparent from these two figures that the minor constituent, lead, is deposited in the grain boundaries in discrete particles 57 sufficiently spaced-apart to preclude the presence of a continuous thick film along the boundary.

To assure that there will be some significant amount of minor constituent available at the grain boundaries, the minimum amount of minor constituent that should be added to the major constituent in the liquid state during preparation of the alloy should substantially exceed the solid state solubility of the minor constituent in the major constituent, considered at the eutectic temperature or the freezing temperature of the minor constituent if there is no eutectic. Otherwise, there would be no significant amount of free minor constituent available for deposit in the grain boundaries when the mixture solidified upon cooling. This we have found seriously detracts from the anti-weld resistance of the contacts. The apparent reason for this will soon be explained in greater detail.

In our initial studies of this matter, copper-bismuth alloys containing bismuth prepared by the process referred to hereina'bove were investigated and found to be inadequate from a dielectric strength viewpoint. The dielectric strength of an interrupter employing such 20% copper-bismuth contacts was 'found to be drastically lower than that of a corresponding interrupter employing pure copper contacts. For example, an interrupter with 20% copper-bismuth contacts was typically found to have a dielectric strength of about 40 to kv., impulse crest voltage, as compared to 100 kv. for an interrupter with pure copper contacts made in substantially the same way and tested under corresponding conditions. It was originally thought that this reduced dielectric strength was due to the presence of pure bismuth in the alloy and that so long as pure bis-muth was present in any quantity, the dielectric strength of the interrupter under similar test conditions would remain at generally the same unacceptably low value. It was, therefore, most unexpected when it was found that critically small percentages of bismuth, i.e., below a value of about 5% by weight, although present in the alloy in substantially pure form, produced no appreciable impairment of the dielectric strength 'as compared to that for pure copper contacts. It is still not completely understood why critically small amounts of minor constituent produce no substantial impairment of dielectric strength, but it is believed that the character of the deposit of minor constituent in the grain boundaries plays an important role in this respect. In this regard, when this deposit is a thick continuous one as with alloys depicted in FIGS. 3-5, it is believed that quantities of the minor constituent wiil find their way to the surface of the contact and form small heads at the surface that are weakly bonded thereto. The presence of such weakly bonded beads at the surface could trigger a dielectric breakdown. It may require weeks or even months for these small weakly bonded beads to be formed on the surface, but even then, impairment of the dielectric strength properties of the interrupter can ordinarily not be tolerated. When the deposit of minor constituent in the grain boundaries is not a thick continuous one, as in FIGS. 68, it is believed that the minor constituent is held more tenaciously within the grain boundaries. This would effectively reduce the likelihood of dielectric breakdown through weakly bonded heads at the contact surface.

If the contact materials of the present invention are to be suitable, particularly from the dielectric strength and anti-weld viewpoints, it is important that the minor constituent of each contact material be well dispersed throughout the contact material so as to avoid localized regions that are either excessively poor or excessively rich in the minor constituent. Avoiding such localized regions is desirable because excessive richness in the minor constituent leads to impaired dielectric strength, as pointed out hereinabove, whereas excessive po-orness in the minor constituent leads to excessively strong welds, as will soon appear more clearly.

This need for a high degree of dispersion accounts for the requirement that the minor constituent be soluble in the major constituent in the liquid phase. This can best be explained by recalling that these contact materials are prepared by mixing the highly purified constituents while both are in the liquid state and by then lowering the temperature of the mixture untilthe constituents reach the solid state. Unless there is uniform mixing of the constituents in the liquid state, then a relatively poor dispersion of the minor constituent will occur when the mixture freezes upon cooling. We have found that a substantial amount of solubility between the constituents in the liquid phase is needed in order to assure relatively uniform mixing between the two constituents and hence a high degree of dispersion.

As the temperature of the mixture is lowered during cooling, the major constituent, due to its higher freezing or melting point, freezes first so that an alloy rich in the minor constituent is still in a liquid state when the grain structure of the major constituent is being established. During the freezing process, as each grain of the major constituent grows about its characteristic nucleus, most of the still-liquid alloy rich in minor constituent is forced 1nto the outer peripheral portion of the growing grain. When the entire grain of major constituent freezes into its final form, the liquid alloy rich in minor constituent is still at the outer periphery of the grain and will therefore be deposited in the boundaries between adjacent grains upon freezing in response to further cooling. Thus, finite amounts of the minor constituent are present in substantially all of the boundaries between adjacent grains of the major constituent, and the result is a relatively high degree of dispersion of the minor constituent throughout the contact material, as is desired.

As pointed out herein-above, the high degree of dispersion enables us to avoid localized regions excessively poor in the minor constituent, and this is desirable from an anti-weld viewpoint. This can be more fully understood by considering what we presently believe to be the mechanism by which welds between the contacts are formed. This mechanism will be explained in connection with those welds which have been found most troublesome, i.e., the welds that are formed during closing of the circuit breaker against heavy currents. In this regard, when the contacts are driven into closed position, they often bounce apart a short distance immediately after initial impact and then rebound toward each other, aided by the closing force applied to the movable contact and by the resilience of the contact-supporting structure. An arc is drawn when the contacts first bounce apart, and this are melts adjacent surface portions of the contacts so that when they reengage, a molten film is present at the interface. When arcing ceases following reengagement, the energy input into the contact interface drops sharply, and the film at the interface thus quickly cools to the solid state. The result is the formation of a weld between the two contacts. The higher the arcing current, the larger the surface area that will be covered by the molten film and, hence, the larger and stronger the weld ordinarily will be. The cooling process that occurs when arcing ceases upon contact reengagement is a highly directional one, since the thin molten film is located between two relatively cold solid masses. Freezing thus proceeds from the two solid liquid interfaces in toward a plane located centrally of the film transverse to the contacts. The freezing is rapid and is probably completed within .010 second. This rapid directional cooling causes the grain structure in the solidified film to assume a columnar form and also causes a segregation of the two constituents of the contact material because of the difference in their freezing temperatures and their low solid state solubility. When freezing begins, one component of the ,material will be the major constituent in an alpha solid form, and the other component will be a still-liquid alloy rich in the minor constituent. As the higher freezing-temperature major constituent freezes first, it displaces the still molten alloy rich in minor constituent toward the hottest region in the center of the weld zone. As the temperature drops, this molten alloy becomes increasingly rich in the minor constituent and eventually freezes at its eutectic temperature or, if there is no eutectic, at the temperature of the minor constituent. Thus, the last region to freeze is rich in the minor constituent, and such freezing occurs in a plane along the interface between the two contacts.

Metallographic studies of the interface region show that with the contact materials of our invention, there is a distinct boundary that extends generally along a single plane transverse to the direction of contact motion. In this generally planar boundary are small particles of the minor constituent. The planar nature of this interface and the presence of the particles of minor constituent along the plane results in a mechanically weak junction along this plane that can be easily fractured when the contacts are driven apart during a subsequent opening operation. In addition, this junction is weaker than the remainder of either contact and the result is that the fracture accompanying contact separation occurs cleanly along this junction without pulling a significant number of large particles from the body of the contact material.

As an illustration of the character of this interface, the photomicrograph of FIG. 11 is provided. This photomicrograph was taken at 750 magnifications in a crosssectional plane generally perpendicular to the interface. Only a single contact is depicted, this contact having first been driven into engagement with its mating contact against a heavy current to produce a weld and having then been separated from the mating contact under nocurrent conditions to break the weld. The cross-section is taken through the region of the broken weld. The material of the contact was copper-bismuth containing 5% bismuth by weight. The plane of the interface is shown at 60 with particles 61 of bismuth located therealong. The columnar grain structure is shown at 62, where particles of bismuth can be seen at 63 between the columnar grains. In breaking the weld, a small particle of the mating contact was inadvertently pulled from the mating contact and is depicted at 64. Although this particle ideally should have remained with the mating contact, it is so small that it does not appreciably detract from the cleanness of the weld fracture. In this regard, it projects from the generally planar surface 60 only about .0007 inch. The particles of bismuth along the portion of surface 60 beneath this particle 64 are particularly evident from FIG. 11.

To insure that there is an ample amount of the minor, or secondary, constituent present along the junction plane between the two contacts, it is important that the minor constituent be highly dispersed throughout the contact material so as to be available for displacement into any interface where a Weld might occur. If no significant amount of minor constituent is available in the region of the weld, the desired weakening of the weld junction will not occur. Thus, a high degree of dispersion of the minor constituent is needed to produce the desired resistance to the formation of objectionable welds.

A number of other factors have an important effect on whether significant amounts of minor constituent will be present at the weld interface to produce the desired weakening. One is the low freezing point of the minor constituent relative to that of the major constituent. This low freezing point enables the minor constituent to remain in the molten state while the major constituent is freezing and thus enables the freezing process to force the minor constituent into the interface between the two contacts as the columnar grains grow toward the interface. With minor constitutents otherwise meeting the requirements set forth hereinabove but having a higher freezing point than the primary constituent, the minor constituent would freeze first, and only the major constituent would be forced into the interface as the columnar grains grow toward the interface. This would result in a relatively strong weld across the contact interface with lesser strength at points spaced from the interface due to the presence of significant amounts of the minor constituent at these points. The result is a weld across the interface difiicult to break and one which fractures along a jagged surface displaced from the interface when it does break.

Another factor that contributes to the presence of minor, or secondary, constituent in the contact interface is the very low solid state solubility of the minor constituent in the major constituent. Because of this very low solubility combined with the lower freezing point of the minor constituent, the minor constituent remains segregated from the major constituent as the major constituent freezes toward the center of the weld. Thus, free minor constituent is forced to the interface and is therefore available at the interface to Weaken the bond. Where there is substantial solubility in the solid state, the amount of free minor constituent at the interface is greatly reduced if not altogether eliminated, and the result is a relatively strong bond across the interface. For example, consider copper-tin alloys and copper-zinc alloys, that is the bronzes and brasses, and copper-silicon, all three of which are characterized by high solid state solubility between the constituents. With these alloys, it has been found that the bond across the interface is stronger than the remainder of the contact material and that strong welds are formed between the contacts. Not only has excessive force been required to break these welds, but the breaks that finally do occur are very jagged and are characterized by large particles being pulled from the mating contact. In contrast, when the contact materials of the present invention are used, much lower forces can be relied upon to break the welds and the welds break cleanly at the interface. The particular materials for which the welds could be broken with the lowest forces were copper-bismuth, copper-lead, silver-bismuth, and silver-lead.

In certain of the acceptable alloys, the elements used in preparing the alloys form intermetallic compounds with each other even though the minor element has little or no solid state solubility in the major element. Typically, where intermetallic compounds are formed by the elements involved, the intermetallic compound and the major constituent form an eutectic mixture that has a freezing point below that of the major constituent. For the purposes of this application, the intermetallic compound c-an be considered as the minor constituent and the effective freezing point of the minor constituent can be considered to be the freezing point of the eutectic mixture. For example, in an alloy prepared from 99% copper and 1% tellurium, by weight, the intermetallic compound Cu Te is formed and appears in the grain boundaries of the as-cast alloy. Cu Te has a freezing point of 1125 C., but the eutectic formed by the intermetallic compound with copper has -a freezing point of 105 1 C. This latter temperature is below the freezing point of pure copper, which is 1083 C. Thus, the effective freezing point of Cu Te, the minor constituent, is below that of the major constituent, copper.

Another factor that affects the Welding properties of the contacts is the electrical conductivity of the contact material. Generally speaking, good electrical conductivity is desirable in order to inhibit welding. To achieve this good electrical conductivity, the major constituent should be a good electrical conductor and solubility of the minor constituent in the major constituent should be low. This low solubility enables the major constituent to retain its high conductivity despite the presence of the minor constituent. If appreciable solubility is present, the conductivity of the major constituent is greatly reduced, e.g., the addition of tin to copper greatly reduces the conductivity of the copper.

The reason that the major constituent must be a nonrefractory metal is that refractory metals have relatively poor current-interrupting ability. In this regard, when an attempt is made to interrupt currents of more than several thousand amperes with refractory metal contacts, the refractory metal thermionically emits electrons after a current zerowhen subjected to the temperatures accompanying these arcs. Such thermionic emission seriously impairs the ability of the vacuum to recover its dielectric strength after a current zero and thus renders the refractory contacts incapable of consistently interrupting more than several thousand amperes at 13.8 kv. For this reason then, refractory metal such as tungsten and molybdenum and alloys thereof are excluded from the present invention,

As compared to thislimited interrupting ability available with refractory metal contacts, we have been able to consistently interrupt much higher currents with contacts 17 and 18 having their regions 30 formed of the materials of our invention. For example, with contacts 17 and 18 having their regions 30 formed of copper alloyed with one percent by weight of bismuth, we have been able to interrupt 15,400 amperes R.M.S. at 15.5 kv. As another example, with contacts 17 and 18 having their regions 30 formed of copper alloyed with one percent by weight of lead, we have been able to interrupt 16,300 amperes R.M.S. at 15.5 kv.

Although the contacts 17 and 18 may be made entirely of the contact materials of our invention, it is to be understood that it is generally sufficient that only the circuit-making and breaking regions 30 be formed of these materials. The remainder of each contact may be formed of another material suitable for interrupting high currents and having good dielectric strength properties, e.g., pure copper. This was the construction of the contacts mentioned in the immediately preceding paragraph.

It is to be further understood that, in its broader aspects, our invention is not limited to the use of identical materials for the regions 30 of both of the two contacts. For example, only one of the contacts need have its circuit-making and breaking region 30 formed of the particular materials of our invention. The circuit-making and breaking region 30 of the second contact may be formed of a dissimilar material, provided that this dissimilar material includes as its major constituent a metal in which the minor constituent of the first contact has a solid-state solubility of less than two percent by weight, considered at the eutectic temperature or at the freezing temperature of the minor constituent if there is no eutectic. For example, one of the contacts can be made of copper alloyed with a few percent of bismuth or lead and the other contact of pure copper. As another example, one of the contacts can be of copper and a few percent of bismuth and the other contact of copper and a few percent of lead. When dissimilar materials are used for the opposed contacts, the low solid-state solubility between the major constituent of one contact and the minor constituent of the other contact helps to preclude objectionable contact-welding by producing a weak interface between the two contacts upon closing.

To permit the desired high temperature bake-out of the interrupter, the contact material should have an effective vapor pressure that is sufficiently low to enable bakeout to be performed at the required temperature without excessive vaporization of the contact material. By excessive vaporization is meant such vaporization as results in the insulating surfaces of the interrupter being impaired by a metallic coating deposited from contact vapor. As a general rule, the effective vapor pressure of the contact material should not exceed l0 mm. of mercury at the bake-out temperature.

The term metal as used in this application with reference to the constituents of the contact materials is not intended to be limited to elemental metals only but to comprehend within its meaning alloys as well. The

, term alloy is intended to comprehend mixtures as well as solid-solution alloys. The term metal is also intended to comprehend within its meaning intermetallic compounds.

Although the invention is particularly applicable to interrupters with voltage ratings of 7.2 kv. and higher and with current ratings of 8000 amperes R.M.S. and higher, the invention in its broader aspects is also applicable to interrupters that have lower voltage and current ratings.

While We have shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects and we, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An alternating-current vacuum-type circuit interrupter having a rated voltage of at least 7.2 kv. comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one [of said contacts having circuit-making and breaking regions formed of an alloy consisting essentially of a nonrefractory metal major constituent having a boiling point less than 3,500 K. and a non-refractory metal minor constituent that (1) has an effective freezing temperature below that of the major constituent (2) has substantial solubility in the major constituent in the liquid state and (3) is soluble in the major constituent in the solid state to a lesser extent than two percent by weight of the alloy, considered at a controlling temperature corresponding to the eutectic temperature or to the freezing teml3 perature of the minor constituent if there is no eutectic, said minor constituent being highly dispersed throughout said alloy and being present in an amount greater than the solid state solubility of the minor constituent in the major constituent at said controlling temperaure and in an amount small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and 36 kv. R.M.S. 6O cycle Withstand voltage, both voltages being measured across said contacts when fully open.

2. The circuit interrupter of claim 1 in which both of said contacts have circuit-making and breaking regions formed of an alloy as defined in claim 1.

3. The circuit interrupter of claim 1 in which the other of said contacts has circuit-making and breaking regions that engage the circuit-making and breaking regions of said one contact when said interrupter is closed, the circuit-making and breaking regions of said other contact being formed of a material that has as its major constituent a meal in which the minor constituent of said one contact has a solid-state solubility of less than two percent by weight of the alloy of said latter two constituents, considered at the eutectic temperature of said latter alloy or the freezing temperature of said minor constituent if there is no eutectic.

4. The vacuum interrupter of claim 1 in which said minor constituent is present in an amount less than about by weight of the alloy.

5. The vacuum type circuit interrupter of claim 1 in which said alloy has a grain structure characterized by juxtaposed grains of major constituent and deposits of minor constituent in the boundaries between the grains, the amount of minor constituent being so small that, typically, particles of minor constituent in the grain boundaries having a thickness of greater than 5X10- inches are sufiiciently spaced to preclude the presence of a continuous thick deposit having a thickness in excess of 5 10 inches.

6. An alternating-current vacuum-type circuit interrupter comprising a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of an alloy consisting essentially of a non-refractory metal major constituent having a boiling point less than 3,500 K. and a nonrefractory metal minor constituent that (1) has an effective freezing temperature below that of the major constituent (2) has substantial solubility in the major constituent in the liquid state and (3) is soluble in the major constituent in the solid state to a lesser extent than 2% by weight of said alloy considered at a controlling temperaure corresponding to the eutectic temperature of said alloy or the freezing temperature of said minor constituent if there is no eutectic, said minor constituent being present in an amount greater than the solid-state solubility of the minor constituent in the major constituent at said controlling temperature, said alloy contact material having a grain structure characterized by juxtaposed grains of major constituent and deposits of minor constituent in the 'boundaries between the grains, the amount of minor constituent being so small that, typically, particles of minor constituent in the grain boundaries having a thickness greater than 5x10- inches are sufficiently spaced to preclude the presence along the grain boundaries of a continuous thick deposit having a thickness in excess of 5 l0 inches.

7. The circuit interrupter of claim 6 in which both of said contacts have circuit-making and breaking regions formed of an alloy as defined in claim 6.

8. The circuit interrupter of claim 6 in which the other of said contacts has circuit-making and breaking regions that engage the circuit-making and breaking regions of said one contact when said interrupter is closed, the circuitmaking and breaking regions of said other contact being for-med of a material that has as its major constituent a metal in which the minor constituent of said one contact has a solid state solubility of less than two percent by weight of the alloy of said latter two constituents, considered at the eutectic temperature of said latter alloy or the freezing temperature of said minor constituent if there is no eutectic.

9. An alternating-current vacuum-type circuit interrupter having a rated voltage of at least 7.2 k.v., comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of an alloy selected from the group consisting essentially of copper-tellurium, copperbismuth, copper-lead, copper-thallium, silver-bismuth, silver-lead, silver-tellurium, aluminum-lead, aluminumindium, and aluminum-tin, the major constituent of each alloy being specified first and the minor constituent second, the minor constituent being highly dispersed throughout the major constituent and being present in an amount greater than its solid state solubility in the major constituent, considered at the eutectic temperature of said alloy or the freezing temperature of the minor constituent if there is no eutectic, and in an amount small enough to maintain the dielectric strength of the interrupter above kv. peak impulse voltage and 36 kv. R.M.S. 60 cycle withstand voltage, both voltages being measured across said contacts when out of engagement, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which the minor constituent of said one contact has a solid-state solubility of less than two percent by weight, considered at the eutectic temperature of an alloy of said major constituent of the other contact and the minor constituent of said one contact or at the freezing temperature of said minor constituent if there is no eutectic.

19. The vacuum interrupter of claim 9 in which the alloy of said one contact has a grain structure characterized by juxtaposed grains of major constituent and deposits of minor constituent in the boundaries between the grains, the amount of minor constituent being so small that, typically, particles of minor constituent in the grain boundaries having a thickness of greater than 5 l0 inches are sufficiently spaced to preclude the presence of a continuous thick deposit having a thickness in excess of 5X10 inches.

11. The vacuum switch of claim 9 in which said minor constituent of said one contact is present in an amount less than about 5% by weight.

12. An alternating-current vacuum-type circuit inter rupter comprising a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuitmaking and breaking regions formed of an alloy selected from the group consisting essentially of copper-tellurium, copper-bismuth, copper-lead, copper-thallium, silverbismuth, silver-lead, silver-tellurium, aluminum-lead, aluminum-indium, and aluminum-tin, the major constituent of each alloy appearing first and the minor constituent second, the minor constituent being present in a form and amount greater than its solid-state solubility in the major constituent at the eutectic temperature or the freezing temperature of the minor constituent if there is no eutectic, said minor constituent being highly dispersed throughout the major constituent, said alloy having a grain structure characterized by juxtaposed grains of major constituent and deposits of minor constituent in the boundaries between the grains, the amount of minor constituent being so small that, typically, particles of minor constituent in the grain boundaries having a thickness of greater than 5 X 10* inches are sutficiently spaced to preclude the presence of a continuous thick deposit having a thickness in excess of 5X10 inches, the other is? of said contacts being formed of a material that has as its primary constituent a metal in which the minor constituent of said one contact has a solid state solubility of less than two percent by weight of an alloy of said primary constituent and said minor constituent, considered at the eutectic temperature of saidlatter alloy or the -freezing temperature of said minor constituent if there is no eutectic.

13. An alternating-current vacuum-type circuit interrupter having a rated voltage of at least 7.2 kv., comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essentially of copper-telltiriurn, the telluriutn being highly dispersed throughoutthe co er in the form of an in termetallic compound and being present in an amount greater than the maximum solid state solubility of said intermetallic compound in copper and in an amount stiiall enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and 36 kv. R.M.S. 60 cycle withstand voltage, both voltages being measured across said contacts when fully open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a primary constituent a metal in which tellurium and said intermetallic compound have a solid state solubility of less than two percent by weight of an alloy of said primary constituent and the tellurium component, considered at the eutectic temperature of said latter alloy or the freezing temperature of the telluriurn component if there is no eutectic.

14. An alternating cutrent vacuum t pe circuit interr pter having a ratd vdltage or at least 72 live, comprising: a pair of contacts that are relatively movable intoand out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essentially of copper-bismuth, the bismuth being highly dispersed throughout the copper and being present in an amount greater than the solid-state solubility of bismuth in copper at the eutectic temperature and in a minor percentage small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and 36 kv. R.M.S. 6O cycle withstand voltage, both voltages beingmeasured across said contacts when fully open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which bismuth has a solid state solubility of less than two percent by weight of an alloy of bismuth and said major constituent, considered at the eutectic temperature of said latter alloy or the freezing temperature of bismuth if there is no eutectic.

15. An alternating-current vacuum-type circuit interrupter having a rated voltage of at least 7.2 kvt, com prising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essentially of copper-lead, the lead being highly dispersed throughout the copper and being present in an amount greater than the solid state solubility of lead in copper at the eutectic temperature and in a minor percentage small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and 36 kv. R.MLS. 60 cycle Withstand voltage, both voltages being measured across said contacts when fully open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which lead has a solid-state solubility of less than two percent by weight of an alloy of lead and said major constituent considered at the eutectic temperature of said latter alloy or the freezing temperature of lead if there is no eutectic.

16 An alternating current vacuum type circuit interrupter having a rated voltage of at least 7.2 kv., comprisingi a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases arid surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essen tially of copper-thallium, the thallium being highly dispersed throughout the copper and being present in a minor percentage greater than the solid state solubility of thallium in copper at the freezing temperature of thallium and in a minor percentage small enough to maintain the dielectric strength of the interrupter above kv. peak impulse voltage and 36 kv. R.M.S. 60 cycle Withstand voltage, both voltages bein'g'measured across said contacts when fully open, the other of said contacts having circuit-making and'breaking regions formed of a material that has as a major constituent a metal in which thallium has a solid state solubility of less than two percent by Weight at the eutectic temperature of an alloy of said metai and thallium or at the freezing temperature of the thallitim if there is no eutectic.

17. An alternating current vacuum type circuit interruptcr having a rated voltage of at least 7.2 kv., comprising: a pair ofcontacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essentially of silver-bismuth, the bismuth being highly dispersed throughout the silver and being present in a minor percentage greater than the solid state solubility of bismuth in silver at the eutectic temperature and in a minor percentage small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and kv, R.M.S. 60 cycle withstand voltage, both voltages being measured across the contacts when fully open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which bismuth has a solid state solubility of less than two percent by weight of an alloy of bismuth and said major constituent considered at the eutectic temperature of said latter alloy or thefreezing temperature of bismuth if there is no eutectic.

18. An alternating current vacuum type circuit interrupter having a rated voltage of at least 7.2 kv., comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essentially of silver-lead, the lead being highly dispersed throughout the silver and being present in a minor percentage greater than the solid state solubility of lead in silver at the eutectic temperature and in a minor percentage small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and 36 kv. R.M.S. ,60 cycle withstand voltage, both voltages being measured across the contacts when fully open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which lead has a solid state solubility of less than two percent by weight of an alloy or" lead and said major constituent considered at the eutectic temperature of said latter alloy or the freezing temperature of lead it there is no eutectic.

19. An alternating current vacuum type circuit interrupter having a rated voltage of at least 72 kv., comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-marzing and breaking regions formed of a material consisting essentially of silver teliurium, the tellurium being highly dispersed throughout the silver in the form of an intermetallic compound, said intermetallic compound being present in an amount greater than the maximum solid state solubility of said intermetallic compound in silver and in a minor percentage small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impuse voltage and 36 kv. R.M.S. 60 cycle Withstand voltage, both voltages being measured across said contacts when fully-open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which said intermetallic compound has a solid state solubility of less than two percent by weight, considered at the eutectic temperature of any alloy of said metal and the tellurium component or at the freezing temperature of the tellurium component if there is no eutectic.

20. An alternating current vacuum type circuit interrupter having a rated voltage of at least 7.2 kv., comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essentially of aluminum-lead, the lead being highly dispersed throughout the aluminum and being present in an amount greater than the solid state solubility of lead in aluminum at the freezing point of lead and in a minor percentage small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and 36 kv. R.M.S. 60 cycle withstand voltage, both voltages being measured across said contacts when fully open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which lead has a solid state solubility of less than two percent by Weight, considered at the eutectic temperature of an alloy of said metal and lead or at the freezing temperature of lead if there is no eutectic.

21. An alternating-current vacuum-type circuit interrupter having a rated voltage of at least 7.2 kv., comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essentially of aluminum-indium, the indium being highly dispersed throughout the aluminum and being present in an amount greater than the solid state solubility of indium in aluminum at the freezing temperature of indium and in a minor percentage small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and 36 kv. R.M.S. 60 cycle withstand voltage, both voltages being measured across said contacts when fully open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which indium has a solidstate solubility of less than two percent by weight, considered at the eutectic temperature of said metal and indium or at the freezing temperature of indium if there is no eutectic.

22. An alternating current vacuum type circuit interrupter having a rated voltage of at least 7.2 kv., comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuit-making and breaking regions formed of a material consisting essentially of aluminum-tin, the tin being highly dispersed through out the aluminum and being present in an amount greater than the solid state solubility of tin in aluminum at the eutectic temperature and in a minor percentage small enough to maintain the dielectric strength of the interrupter above 95 kv. peak impulse voltage and 36 kv. R.M.S. cycle withstand voltage, both voltages being measured across said contacts when fully open, the other of said contacts having circuit-making and breaking regions formed of a material that has as a major constituent a metal in which tin has a solid state solubility of less than two percent by weight, considered at the eutectic temperature of an alloy of said metal and tin or the freezing temperature of tin if there is no eutectic.

23. An alternating-current vacuum-type circuit interrupter comprising: a pair of contacts that are relatively movable into and out of engagement, said contacts being substantially free of absorbed gases and surface contaminants, at least one of said contacts having circuitmaking and breaking regions formed of a material consisting essentially of a non-refractory metal major constituent having a boiling point less than 3,500 and a nonrefractory metal minor constituent that (1) has an effective freezing temperature below that of the major constituent (2) has substantial solubility in the major constituent in the liquid state and (3) is soluble in the major constituent in the solid state to a lesser extent than two percent by weight of an alloy of the major and minor constituents, considered at a controlling temperature corresponding to the eutectic temperature of said alloy or the freezing temperature of said minor constituent if there is no eutectic, said minor constituent being highly dispersed throughout said material and being present in an amount greater than the solid state solubility of the minor constituent in the major constituent at said controlling temperature, the amount of said minor constituent being below about five percent by weight of said material.

References Cited by the Examiner UNITED STATES PATENTS 1,385,223 7/1921 Milliken 138 2,026,546 1/1936 Kempf et a1 75-138 2,143,824 1/1939 Smith 75163 2,162,362 6/ 1939 Smith 751S3 2,178,508 10/1939 Zickrick 200-166 2,246,328 6/1941 Smith 75-153 2,268,939 1/ 1942 Hensel 75-153 2,602,095 7/ 1952 Faus 75173 2,801,917 8/1957 Buttner et al. 75138 2,975,256 3/1961 Lee et al 200--166 3,014,110 12/1961 Cobine 200166 BENJAMIN HENKIN, Primary Examiner. HYLAND BIZOT, Examiner. 

1. AN ALTERNATING-CURRENT VACUUM-TYPE CIRCUIT INTERRUPTER HAVING A RATED VOLTAGE OF AT LEAST 7.2 KV. COMPRISING: A PAIR OF CONTACTS THAT ARE RELATIVELY MOVABLE INTO AND OUT OF ENGAGEMENT, SAID CONTACTS BEING SUBSTANTIALLY FREE OF ABSORBED GASES AND SURFACE CONTAMINANTS, AT LEAST ONE OF SAID CONTACTS HAVING CIRCUIT-MAKING AND BREAKING REGIONS FORMED OF AN ALLOY CONSISTING ESSENTIALLY OF A NONREFRACTORY METAL MAJOR CONSTITUENT HAVING A BOILING POINT LESS THAN 3,500*K. AND NON-REFRACTORY METAL MINOR CONSTITUENT THAT (1) HAS AN EFFECTIVE FREEZING TEMPERATURE BELOW THAT OF THE MAJOR CONSTITUENT (2) HAS SUBSTANTIAL SOLUBILITY IN THE MAJOR CONSTITUENT IN THE LIQUID STATE AND (3) IS SOLUBLE IN THE MAJOR CONSTITUENT IN THE SOLID STATE TO A LESSER EXTENT THAN TWO PERCENT BY WEIGHT OF THE ALLOY, CONSIDERED AT A CONTROLLING TEMPERATURE CORRESPONDING TO THE EUTECTIC TEMPERATURE OR TO THE FREEZING TEMPERATURE OF THE MINOR CONSTITUENT IF THERE IS NO EUTECTIC, SAID MINOR CONSTITUENT BEING HIGHLY DISPERSED THROUGHOUT SAID ALLOY AND BEING PRESENT IN AN AMOUNT GREATER THAN THE SOLID STATE SOLUBILITY OF THE MINOR CONSTITUENT IN THE MAJOR CONSTITUENT AT SAID CONTROLLING TEMPERATURE AND IN AN AMOUNT SMALL ENOUGH TO MAINTAIN THE DIELECTRIC STRENGTH OF THE INTERRUPTER ABOVE 95 KV. PEAK IMPULSE VOLTAGE AND 36 KV. R.M.S. 60 CYCLE WITHSTAND VOLTAGE, BOTH VOLTAGES BEING MEASURED ACROSS SAID CONTACTS WHEN FULLY OPEN. 